Personal pulmonary function analyzers

ABSTRACT

A personal pulmonary function analyzer comprises a generally elongate body which defines a flow passageway extending between an opening at one end of the body and an opening at a side of the body. The flow passageway can be less than 10 cm in length, and is conveniently about 3 cm in length.

TECHNICAL FIELD

The invention relates to personal pulmonary function analyzers, andparticularly to pulmonary function analyzers which are sufficientlyportable to be carried by a user.

BACKGROUND OF THE INVENTION

Lung function depends on the ease with which air passes from theatmosphere to the alveoli (air sacs) and back to the atmosphere again.This is mainly determined by the flow resistance of the small airways ofthe lungs. Lung function can vary considerably over short periods oftime, and can be affected by such factors as temperature, humidity,exercise and disease, such as asthma. For example, a person playing asport may suddenly become short of breath as a result of a sport-inducedbronchiospasm, in which the bronchial tubes contact due to exertion.Asthma sufferers are also particularly vulnerable to allergens, virusesand smoke.

Although portable peak-flow meters are available at low price, theirusefulness in analyzing lung function is limited. Such peak-flow metersare prone to significant errors, which are particularly undesirable inthe case where the meters are used to regulate a drug treatment for apulmonary disorder. Known low price peak-flow meters are based onmechanical friction spring arrangements, which are uncalibrated, andintended to provide relative results only. Such devices are often usedto regulate a user's intake of steroids, which provide a preventativetreatment for asthma. It will be appreciated that an incorrect readingfrom the peak-flow device will result in the user's taking an incorrectdose of steroids, either too much or too little, which is undesirableand potentially dangerous.

In order to carry out accurate pulmonary function tests, it is normallynecessary for the patient's lung function to be tested in the hospitalusing non-portable testing equipment. However, in view of the fact thatasthma, particularly in the case of asthma suffers who are children, isbelieved often to contain a psychosomatic element, tests which arecarried out in the hospital do not always give representative results.This is because the mere fact that a patient has to attend the hospitaltends to increase the stress level of the patient, and this in turnleads to less reliable test results. Lung function is very changeableover short periods of time, e.g. before and during exercise. To get acomplete picture of a person's lung function, multiple measurements overtime need to be taken during normal day-to-day activities. At present,testing a patient in the hospital is often the only way of carrying outthe full range of appropriate tests.

Such tests result in a variety of useful measurements, the five mostsignificant of which are summarized below.

PEAK FLOW is the simplest measurement, and is simply an indication ofthe peak velocity of expelled air expressed in liters per minute. Thismeasurement, like the other measurements discussed below, is typicallyobtained by asking the patient to blow into suitable apparatus.

VC is the total volume of expelled air, expressed in liters.

FEV1 is the volume of air expelled in the first second, expressed inliters.

FEV1/VC is the volume of air expelled in the first second divided by thetotal volume expelled, expressed as a percentage.

FEF25%-75% is the average velocity of air flow between 25% expelledvolume and 75% expelled volume, expressed in liters per minute.

Devices for carrying out the above measurements typically involve thepatient's blowing through a tube containing a restriction, and takingpressure measurements on each side of the restriction. The restrictionis often in the form of one or more gauzes or meshes, which have theeffect of reducing the chaotic behavior of the air flow through thepipe. A portable device which operates on the basis of pressuremeasurements on either side of a flow restriction is described inAustralian Patent Application No. 67994/90. FIG. 1 of that applicationshows a hand-held device (see FIG. 1), the upper part of which isprovided with a straight tube 16 along which the user blows air in orderto obtain PEAK FLOW and FEV1 measurements. These measurements areobtained by measuring the pressure on either side of a restrictionwithin the tube 16, as shown in FIG. 5. Although the device is portable,the device cannot easily be carried in a pocket. This is due in part tothe length of the tube 16 of the manufactured article, which is around12 cm. In the prior art, lengths of this size or greater have beenfavored in order to reduce the chaotic behavior of the air flow withinthe tube, thus making reliable pressure measurements within the tubemore easy to carry out.

The invention seeks to provide an improved personal pulmonary functionanalyzer, and an improved method of performing flow measurements in apersonal pulmonary function analyzer.

DISCLOSURE OF INVENTION

According to the invention there is provided a personal pulmonaryfunction analyzer comprising a generally elongate body which defines aflow passageway extending between a first opening at one end of the bodyand a second opening at a side of the body, wherein the flow passagewayextends along a curve between the first and second openings, and whereinthe second opening opens directly to the atmosphere.

It will be appreciated that, because the flow passageway does not passalong the whole length of the body, the body is able to be made morecompact.

Advantageously, there are no obstructions within the flow passagewayother than a pressure measurement tube. This is convenient as it allowsthe flow passageway to be easily cleaned, and has minimum effect on theflow of air through the passageway.

The invention also provides a method of measuring the flow rate withinthe flow passageway of a personal pulmonary function analyzer, themethod comprising measuring the pressure at a location within the flowpassageway, measuring the ambient air pressure around the analyzer, andcomparing the two pressure measurements, the method being carried out ina personal pulmonary function analyzer as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be more particularly described, byway of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of the body of a personal pulmonaryfunction analyzer in accordance with the invention;

FIG. 2 is a plan view of the upper side of the upper part of the body;

FIG. 3 is a side view of the upper part;

FIG. 4 is a plan view of the lower side of the upper part;

FIG. 5 is an end view of the upper part;

FIG. 6 is a plan view of the upper side of the lower part of the body;

FIG. 7 is a side view of the lower part;

FIG. 8 is a plan view of the lower side of the lower part;

FIG. 9 is an end view of the lower part;

FIG. 10 is an enlarged view of the flow passageway region of the lowerpart shown in FIG. 6; and

FIG. 11 is a flow diagram showing the basic operation of the analyzer.

BEST MODE FOR CARRYING OUT THE INVENTION

The body 2 of the personal pulmonary function analyzer is shown in FIG.1, and defines a flow passageway 4 which extends between an inputopening 6 and an output opening 8. The body 2 is elongate, and has anupper surface 10 provided with a transparent window 12 and a button 14.An LCD (not shown) is located below the window 12, and provides areadout of the various measurements which can be carried out using theanalyzer. The operation of the button 14 will be described below. Thewindow 12 and button 14 are sealed, so that the entire analyzer can besubmerged under water without damage, The input opening 6 is located atthe opposite end of the body 2 to the button 14, and the flow passageway4 is curved so that the output opening 8 is located on a side wall 16 ofthe body 2.

It will be appreciated that such a design allows the pulmonary functionanalyzer to be considerably reduced in size, in view of the fact thatthe flow passageway 4 passes through only a small portion of the body 2.Hitherto, it has been thought necessary to provide as straight a flowpassageway as possible in order to reduce the chaotic-behavior of theair flow within the passageway. Various other measures, such as thegauzes and meshes described above, were also employed in the prior artin order to reduce chaotic behavior. The provision of a curved flowpassageway 4 therefore represents a significant departure from currentthinking in the art.

Furthermore, the length of the flow passageway 4, measured along thecenter of the flow passageway 4, is only about 3 cm. Such a short flowpassageway 4 results in some chaotic behavior of the air in thepassageway 4. However, it has been found that the resulting variationsin pressure measurements within the flow passageway 4 can be overcome byfiltering and averaging the pressure samples using appropriate software.

The body 2 is formed from an upper part 17, shown in FIGS. 2 to 5, and alower part, shown in FIGS. 6 to 9. Referring to FIG. 4, the upper partdefines the upper half of the flow passageway 4, together with the upperhalf of a tube socket 18. The tube socket 18 is adapted to hold a flowmeasurement tube 20 shown in FIG. 10. The tube socket 18 opens at oneend into the flow passageway 4, and opens at the other end into aconduit 22, which is in turn connected to a pressure transducer opening24. When the analyzer is assembled, the opening 24 opens onto one sideof a solid state pressure transducer (not shown). The conduit 22 is alsovisible as a protrusion on the upper side of the upper part, as shown inFIG. 2.

The other side of the solid state pressure transducer is exposed toambient air pressure via a grilled opening 26 in the lower part 28 ofthe body 2. as shown in FIG. 8. The lower part 28 defines the lower partof the flow passageway 4 and the lower part of the tube socket 18, asshown in FIG. 6 The lower part 28 also defines an enclosure 30 withinwhich the solid state transducer is housed. A number of prorusions 32are also provided to support the PCB (not shown) which sits below thetransparent window 12 as described above, arid on which the LCD ismounted.

FIG. 10 is an enlargement of a portion of FIG. 6. The flow measurementtube 20 is directed generally perpendicular to the longitudinal axis ofthe body 2, and projects from the socket 18 into the flow passageway 4.The tube 20 is cylindrical, and provided with a slanted opening 34 atone end thereof. The opening 34 is thus directed in the downstreamdirection of the flow passageway 4 so that when the user blows into theinput opening 6 a vacuum or low pressure region is produced adjacent theopening 34. The vacuum is passed to the solid state pressure transducervia the conduit 22, and a comparison is made with the ambient pressure.

The operation of the personal pulmonary function analyzer will now bedescribed with reference to the flow diagram shown in FIG. 11.

At step 1, the button 14 is pressed, and a microcontroller (not shown)within the body 2 is supplied by internal lithium cells with enoughpower to switch on. The microcontroller is a conventional device, whichcontains its own RAM and ROM.

At step 2, the microcontroller is initialized, and its registers arereset, as are data values. Processor speed and periodic interruptinformation is set. The periodic interrupt occurs 100 times per second,which is thus the sampling rate of the device.

At step 3, the pulmonary function analyzer calibrates itself by taking50 pressure samples, and filtering these samples using appropriatesoftware to produce a running average of the samples. The pressure inthe flow passageway 4 when the user is not blowing through the flowpassageway 4 is therefore sampled 50 times in order to produce a zeroreference pressure. The zero reference pressure is simply the runningaverage result of the 50th sample.

At step 4, the LCD displays, through the window 12, the word READY, andthe analyzer then enters a loop 5 in which the pressure in the flowpassageway 4 is sampled 100 times per second in order to detect whetherthe user is blowing into the input opening 6. The threshold for thisdetection is chosen to be any suitable pressure measurement in excess ofthe zero reference calculated in step 3. In the present embodiment, avalue of two sample points is used as the trigger. That is, the pressuredetected by the flow measurement tube 20 must increase by two of thesmallest units which the device can measure in order to exceed thethreshold.

Once the threshold has been exceeded, as a result of the user blowinginto the flow passageway 4, the pressure in the flow passageway 4 issampled every 100th of a second for four seconds, as shown in step 6 ofFIG. 11. The sampled values are stored in the memory of the device, andfiltered using appropriate software.

At step 7, sampling of the pressure in the flow passageway 4 is stopped(thus saving battery power), and the results are calculated by themicrocontroller. The microcontroller is able to calculate the fivepulmonary measurements described above, namely, PEF25%-75%, FEV1, PEAKFLOW, VC and FEV1/VC. One of the those quantities is displayed throughwindow 12 at step 8, and each press of the button 14 (step 9) causes thenext quanuty to be displayed through the window 12.

At any time, if button 14 is held down for more than 1.5 seconds, theunit is reset, and the above process is restarted. In order to preservethe battery, the unit automatically switches off after about 12 secondsof idle time.

The foregoing describes only preferred embodiments of the presentinvention, and modifications, obvious to those skilled in the art, canbe made thereto without departing from the scope of the presentinvention.

We claim:
 1. A personal pulmonary function analyzer comprising agenerally elongate body having two ends and a side extending betweensaid two ends, a flow passageway extending between a first openinglocated at one said end of the body and a second opening located at saidside of the body intermediate said two ends, the flow passagewayextending along a curve between the first and second openings, thesecond opening directly to the atmosphere, and passageway pressuremeasurement means extending at least partially into said curved flowpassageway for measuring the pressure within said curved flowpassageway.
 2. A personal pulmonary function analyzer as claimed inclaim 1, wherein said first opening of the flow passageway, at said endof the body, is an input opening into which a user blows when using theanalyzer.
 3. A personal pulmonary function analyzer as claimed in claim1, wherein the flow passageway is smoothly curved between said first andsecond openings.
 4. A personal pulmonary function analyzer as claimed inclaim 3, wherein the flow passageway is smoothly curved between saidfirst and second openings along most of the length of the flowpassageway.
 5. A personal pulmonary function analyzer as claimed inclaim 3, wherein the flow passageway is smoothly curved between saidfirst and second openings along the whole of the length of the flowpassageway.
 6. A personal pulmonary function analyzer as claimed inclaim 1, wherein the analyzer further comprises pressure comparisonmeans connected to said passageway pressure measurement means forcomparing said pressure within the flow passageway with the ambient airpressure around the analyzer.
 7. A personal pulmonary function analyzeras claimed in claim 1, wherein the passageway pressure measurement meanscomprises a tube which extends into the flow passageway, and which has apassageway opening at the end thereof which opens into the flowpassageway.
 8. A personal pulmonary function analyzer as claimed inclaim 7, wherein said passageway opening is slanted with respect to thetube so as to face in the downstream direction of the flow passageway.9. A personal pulmonary function analyzer as claimed in claim 7, whereinthere are no obstructions within the flow passageway other than thetube.
 10. A personal pulmonary function analyzer as claimed in claim 1,wherein the flow passageway is not more than 10 cm in length.
 11. Apersonal pulmonary function analyzer as claimed in claim 10, wherein thelength of the flow passageway is less than 7.5 cm.
 12. A personalpulmonary function analyzer as claimed in claim 10, wherein the lengthof the flow passageway is less than 5 cm.
 13. A personal pulmonaryfunction analyzer as claimed in claim 10, wherein the length of the flowpassageway is around 3 cm.
 14. A method of measuring the flow ratewithin the flow passageway of a personal pulmonary function analyzerwhich includes a generally elongate body having two ends and a sideextending between said two ends, a flow passageway extending between afirst opening located at one said end of the body and a second openinglocated at said side of the body intermediate said two ends, the flowpassageway extending along a curve between the first and secondopenings, the second opening opening directly to the atmosphere, themethod comprising measuring the pressure at a location within the curvedflow passageway, measuring the ambient air pressure around the analyzer,and comparing the two pressure measurements.